In the art of integrated circuit design, to improve the reusability, standard cells are often laid out and saved in a circuit library. When an integrated circuit is designed, the standard cells are retrieved from the circuit library, and are placed and routed. The placement is performed using a computer, which runs a tool for designing integrated circuits. The standard cells are placed as a plurality of rows that are parallel to each other. The edges of some standard cells may be abutted. Other standard cells, however, cannot be abutted. In these cases, filler cells are inserted between the standard cells in order to separate the standard cells from each other. The introduction of the filler cells, however, results in the chip area to be wasted.